Transmit diversity framing structure for multipath channels

Abstract

Systems and techniques are disclosed for framing and processing single-carrier and/or OFDM transmit-diversity transmissions through delay-spread channels, as well as for deframing and processing the corresponding merged signals, received from a plurality of antennas, to estimate the transmitted information. Time-domain processing techniques may be used for both types of transmissions to create multiplexed dual signal-unit pairs, particularly when cyclic prefixes are needed to reduce delay-spreading effects. Repetitive pilot words may be employed in burst preambles and/or in payloads of transmission bursts to minimize or provide flexibility in the amount of bandwidth that is consumed to generate good channel response estimates under changing channel conditions.

What is claimed is:  
     
         1 . A method of transmitting dual signal-unit pairs from diverse antennas, comprising 
 a) deriving a first N-point signal unit from a first portion of source data, and deriving a second N-point signal unit from a second portion of source data,    b) processing in the time domain to 
 i) establish a complex conjugated and modulo-N time-inverted form of the first N-point signal unit as a first variant signal unit,  
 ii) establish a negative complex conjugated and modulo-N time-inverted form of the second N-point signal unit as a second variant signal unit, and  
 iii) prepend a corresponding cyclic prefix on each signal unit to form a prefixed first signal unit, a prefixed first variant signal unit, a prefixed second signal unit, and a prefixed second variant signal unit;  
   c) transmitting, substantially concurrently, the prefixed first signal unit from a first antenna and the prefixed second variant signal unit from a second antenna, and    d) transmitting, substantially concurrently, the prefixed second signal unit from the first antenna and the prefixed first variant signal unit from the second antenna.    
     
     
         2 . The method of  claim 1 , wherein each N-point signal unit is an N-point OFDM symbol.  
     
     
         3 . The method of  claim 1 , wherein each N-point signal unit is a block of N time-domain samples.  
     
     
         4 . The method of  claim 3 , wherein the time domain samples are samples from a single carrier modulation system.  
     
     
         5 . The method of  claim 1 , further comprising: 
 e) transmitting a pilot word from the diverse antennas by 
 i) establishing an M-point first pilot signal unit expected by a receiver and an M-point first variant pilot signal unit that is a form of the first pilot signal modified by complex conjugation,  
 ii) establishing an M-point second pilot signal unit expected by the receiver and an M-point second variant pilot signal unit that is a form of the second pilot signal modified by both complex and real conjugation,  
 iii) cyclically prefixing each pilot signal unit to form a prefixed first pilot signal unit, a prefixed first variant pilot signal unit, a prefixed second pilot signal unit, and a prefixed second variant pilot signal unit,  
 iv) substantially concurrently transmitting the prefixed first pilot signal unit and the prefixed second variant pilot signal unit from the diverse antennas, and  
 v) substantially concurrently transmitting the prefixed second pilot signal unit and the prefixed first variant pilot signal unit from the diverse antennas.  
   
     
     
         6 . The method of  claim 5 , wherein J is an integer greater than one and/or P is an integer greater than one and step (e) further comprises: 
 vi) transmitting from the diverse antennas, immediately subsequent to step (e)(iv), (J−1) repetitions of the first pilot signal unit and (J−1) repetitions of the second variant pilot signal unit, and    vii) transmitting from the diverse antennas, immediately subsequent to step (e)(v), (P−1) repetitions of the second pilot signal unit and (P−1) repetitions of the first variant pilot signal unit.    
     
     
         7 . The method of  claim 6 , wherein J=P.  
     
     
         8 . The method of  claim 6 , wherein each cyclic prefix is identical to the pilot signal unit that it prefixes.  
     
     
         9 . The method of  claim 5 , further comprising: 
 f) transmitting payload elements by performing steps (a), (b), (c) and (d) wherein: 
 i) the first and second signal units are payload signal units unknown to a receiver,  
 ii) L is a payload signal unit size, N=L, and  
 iii) L=M.  
   
     
     
         10 . The method of  claim 6 , further comprising: 
 f) transmitting payload elements by performing steps (a), (b), (c) and (d) wherein: 
 i) the first and second signal units are payload signal units unknown to a receiver,  
 ii) L is a payload signal unit size, N=L, and  
 iii) L is not equal to M.  
   
     
     
         11 . The method of  claim 5 , further comprising: 
 f) transmitting data in a frame structure that includes a burst preamble followed by a payload;    g) incorporating, within the burst preamble, the pilot word transmission of step (e) modified in that M PRE  is a preamble pilot signal unit size, and M=M PRE ; and    h) transmitting payload elements within the payload by performing steps (a), (b), (c) and (d) wherein: 
 i) the first and second signal units are payload signal units containing data that may be unknown to a receiver before decoding, and  
 ii) L is a payload signal unit size, and N=L.  
   
     
     
         12 . The method of  claim 11 , further comprising: 
 j) transmitting a further pilot word within the payload as a payload pilot word by performing step (e) modified in that M PAY  is a payload pilot signal unit size, and M=M PAY .    
     
     
         13 . The method of  claim 12 , further comprising: 
 k) transmitting a pilot word having a repetitive pilot signal unit, by 
 i) including, as part of the preamble pilot word transmission of step (g), the steps of  claim 5  modified in that J=J PRE  and P=P PRE , or  
 ii) including, as part of the payload pilot word transmission of step (j), the steps of  claim 5  modified in that J=J PAY  and P=P PAY .  
   
     
     
         14 . The method of  claim 13 , wherein J PRE ≠J PAY  and/or P PRE ≠P PAY .  
     
     
         15 . The method of  claim 13 , further comprising varying, in response to changes in an indication of channel condition, the value of one or more of the group consisting of J PRE , J PAY , P PRE  and P PAY .  
     
     
         16 . The method of  claim 5 , further comprising varying a time frequency at which step (e) is performed in response to changes in an indication of channel condition.  
     
     
         17 . The method of  claim 5 , further comprising varying a value of M in accordance with changes in an indication of channel condition.  
     
     
         18 . The method of  claim 6 , further comprising varying a value of J and/or a value of P in accordance with changes in an indication of channel condition.  
     
     
         19 . A method of interpreting signals received by a receiver that were transmitted in multiplexed forms from diverse transmit antennas, the method comprising: 
 a) identifying a received pilot word that includes a first M-point pilot signal unit preceded by a cyclic prefix corresponding thereto, and a second M-point pilot signal unit preceded by a cyclic prefix corresponding thereto;    b) determining 
 i) a first pilot received signal unit PR 0  by using the first M-point pilot signal unit, after discarding the corresponding cyclic prefix, and  
 ii) a second pilot received signal unit PR 1  by using the second M-point pilot signal unit, after discarding the corresponding cyclic prefix;  
   c) producing 
 i) a first channel estimate H˜ 0  of a first channel response H 0  by combining forms of PR 0  and PR 1  in a first manner with forms of corresponding expected pilot signal units ES 0  and ES 1 , and  
 ii) a second channel estimate H˜ 1  of a second channel response H 1  by combining forms of PR 0  and PR 1  in a different second manner with forms of ES 0  and ES 1 ;  
   d) receiving a payload element that includes a first L-point received payload signal unit R 0  and a second received payload signal unit R 1 ;    e) combining forms of H˜ 0  and H˜ 1  with forms of R 0  and R 1  to obtain a first L-point combined signal unit C 0  and a second L-point combined signal unit C 1 ; and    f) deriving, from C 0  and C 1 , estimates S˜ 0  and S˜ 1  of L-point transmitted payload signal units S 0  and S 1 .    
     
     
         20 . The method of  claim 19 , wherein J and/or P are greater than one, and step (a) further comprises: 
 i) receiving J substantially similar sequential M-point pilot signal units beginning with the first M-point pilot signal unit, and    ii) receiving P substantially similar sequential M-point pilot signal units beginning with the second M-point pilot signal unit.    
     
     
         21 . The method of  claim 20 , wherein step (b)(i) further comprises averaging valid ones of the J substantially similar sequential M-point pilot signal units to establish the first pilot received signal unit PR 0 , and step (b)(ii) further comprises averaging valid ones of the P substantially similar sequential M-point pilot signal units to establish the second pilot received signal unit PR 1 .  
     
     
         22 . The method of  claim 21 , wherein M=L.  
     
     
         23 . The method of  claim 19 , wherein M<L, and step (c) further comprises interpolating M-point information with an interpolation filter to establish L-point channel estimate information for L-point channel estimates H˜ 0  and H˜ 1 .  
     
     
         24 . The method of  claim 19 , wherein the received payload signal units R 0  and R 1  are L-point OFDM symbols.  
     
     
         25 . The method of  claim 19 , wherein the received payload signal units R 0  and R 1  are L-sample blocks of single-carrier signals.  
     
     
         26 . The method of  claim 19 , wherein step (f) further comprises multiplying C0 and C1 by an equalization function derived using Zero Forcing or Minimum Mean Squared Error optimization criteria.  
     
     
         27 . The method of  claim 19 , further comprising 
 g) identifying a frame for a received signal burst including a burst preamble portion and a payload portion;    h) deriving preamble channel estimates by performing, for a signal within the burst preamble portion, steps (a), (b) and (c) wherein M=M PRE , PR 0 =P PRE R 0 , PR 1 =P PRE R 1 , ES 0 =E PRE S 0 , and ES 1 =E PRE S 1 ;    i) estimating a multiplicity of payload signal units by performing steps (d), (e) and (D repetitively for first payload signals within the payload portion;    j) deriving payload channel estimates by performing, for a signal within the payload portion and subsequent to the first payload signals, steps (a), (b) and (c) wherein M=M PAY , PR 0 =P PAY R 0 , PR 1 =P PAY R 1 , ES 0 =E PAY S 0 , and ES 1 =E PAY S 1 .    
     
     
         28 . The method of  claim 27 , wherein M PAY ≠M PRE .  
     
     
         29 . The method of  claim 27 , wherein J PRE  and/or P PRE  are greater than one, and step (h) further comprises: 
 i) receiving J PRE  substantially similar sequential M PRE -point pilot signal units beginning with the first M PRE -point pilot signal unit, and    ii) receiving P PRE  substantially similar sequential M PRE -point pilot signal units beginning with the second MPRE-point pilot signal unit.    
     
     
         30 . The method of  claim 29 , wherein each cyclic prefix of M PRE -point pilot signal units is an M PRE -point signal unit.  
     
     
         31 . The method of  claim 27 , wherein J PAY  and/or P PAY  are greater than one, and step (h) further comprises: 
 i) receiving J PAY  substantially similar sequential M PAY -point pilot signal units beginning with the first M PAY -point pilot signal unit, and    ii) receiving P PAY  substantially similar sequential M PAY -point pilot signal units beginning with the second M PAY -point pilot signal unit.    
     
     
         32 . The method of  claim 31 , wherein each cyclic prefix of M PAY -point pilot signal units is an M PAY -point signal unit.  
     
     
         33 . The method of  claim 31 , further comprising: 
 k) adapting channel estimate quality in response to changing channel conditions by 
 i) sharing reception quality information between the receiver and the transmitter, and  
 ii) varying, in response to changes in the reception quality information, a value of one or more pilot word parameters from a group of parameters consisting of 
 (A) a frequency of payload pilot word transmissions,  
 (B) M PAY ,  
 (C) J PAY ,  
 (D) P PAY ,  
 (E) M PRE ,  
 (F) J PRE , and  
 (G) P PRE .  
 
   
     
     
         34 . A method of transmitting dual signal-unit pairs from diverse antennas, comprising: 
 a) deriving a first M-point pilot signal unit from a first portion of pilot data expected by a receiver, and deriving a second M-point pilot signal unit from a second portion of pilot data expected by the receiver;    b) establishing a complex conjugated form of the first pilot signal unit as a first variant pilot signal unit, and a negative complex conjugated form of the second pilot signal unit as a second variant pilot signal unit;    c) prependiing a corresponding cyclic prefix on each of the pilot signal units of steps (a) and (b) to form a prefixed first pilot signal unit, a prefixed second pilot signal unit, a prefixed first variant pilot signal unit, and a prefixed second variant pilot signal unit;    d) transmitting, substantially concurrently, the prefixed first pilot signal unit from a first antenna and the prefixed second variant pilot signal unit from a second antenna;    e) transmitting, substantially concurrently, the prefixed second pilot signal unit from the first antenna and the prefixed first variant pilot signal unit from the second antenna;    f) transmitting a repetitive pilot signal unit without a preamble, where J and/or P is an integer greater than 1, by 
 i) transmitting, (J−1) times immediately subsequent to step (d), the first pilot signal unit from a first antenna and the second variant pilot signal unit substantially concurrently from a second antenna, and  
 ii) transmitting, (P−1) times immediately subsequent to step (e), the second pilot signal unit from the first antenna and the first variant pilot signal unit substantially concurrently from the second antenna.  
   
     
     
         35 . The method of  claim 34  wherein each M-point pilot signal unit is an M-point OFDM symbol.  
     
     
         36 . The method of  claim 34  wherein each M-point pilot signal unit is a block of M samples of a single-carrier signal.  
     
     
         37 . A system for transmitting dual signal-unit pairs from diverse antennas, comprising 
 a) first and second antennas;    b) a signal-unit derivation block configured to derive N-point signal-units of time-domain samples from modulated source information;    c) a diversity multiplexer block configured to multiplex pairs of the derived N-point signal units into multiplexed dual signal-unit pairs, each multiplexed dual signal-unit pair including a first and a second N-pdint multiplexed-signal-unit (“MSU”) for the first antenna and a first and a second N-point MSU for the second antenna, wherein: 
 i) the first N-point MSU for the first antenna is related to the second N-point MSU for the second antenna by complex conjugation and modulo-N sample time inversion, and  
 ii) the second N-point MSU for the first antenna is related to the first N-point MSU for the second antenna by complex conjugation, negation, and modulo-N sample time inversion;  
   d) a first output processing block configured to cyclically prefix the first and second N-point MSUs for the first antenna, and to process the prefixed MSUs for sequential transmission from the first antenna; and    e) a second output processing block configured to cyclically prefix the first and second N-point MSUs for the second antenna, and to process the prefixed MSUs for sequential transmission from the second antenna substantially concurrently with the sequential transmission from the first antenna.    
     
     
         38 . The system of  claim 37 , wherein the signal-unit derivation block (b) further comprises an inverse Fourier transform block configured to produce the N-point signal-units from N-point OFDM symbols derived from the modulated source information.  
     
     
         39 . The system of  claim 37 , wherein the time domain samples are samples from a single carrier modulation system.  
     
     
         40 . The system of  claim 37 , further comprising (f) a burst organization block configured to introduce one or more pilot words expected by a receiver into a signal stream of information not known to the receiver to form a burst stream of information, such that at least one cyclically prefixed pilot word dual MSU pair is transmitted substantially concurrently from the diverse antennas at an expected relative position within a transmission burst of multiple dual MSU pairs conveying the burst stream of information.  
     
     
         41 . The system of  claim 40 , wherein J and P are positive integers, J≠1 and/or P≠1, and further comprising (g) a pilot word construction block configured to establish the pilot words such that the at least one cyclically prefixed pilot word dual MSU pair includes: 
 i) a first cyclically prefixed pilot word MSU for the first antenna, having a cyclic prefix prepended to J sequential copies of a first pilot subword,  
 ii) a second cyclically prefixed pilot word MSU for the first antenna, having a cyclic prefix prepended to P sequential copies of a second pilot subword,  
 iii) a first cyclically prefixed pilot word MSU for the second antenna, having a cyclic prefix prepended to J sequential copies of a subword related to the first pilot subword by complex conjugation, real value inversion, and sample time inversion, and  
 iv) a second cyclically prefixed pilot word MSU for the second antenna, having a cyclic prefix prepended to P sequential copies of a subword related to the second pilot subword by complex conjugation and sample time inversion.  
 
     
     
         42 . The system of  claim 41 , wherein J=P.  
     
     
         43 . The system of  claim 41 , wherein each pilot word cyclic prefix is identical to the pilot subword that it prefixes.  
     
     
         44 . The system of  claim 40 , wherein payload dual MSU pairs convey information not know to the receiver prior to transmission, and a first cyclically prefixed pilot word dual MSU pair precedes, within the burst stream of information, all payload dual MSU pairs.  
     
     
         45 . The system of  claim 44 , wherein a second cyclically prefixed pilot word dual MSU pair follows, within the burst stream of information, at least one payload dual MSU pair.  
     
     
         46 . The system of  claim 45 , wherein the first and second cyclically prefixed pilot word dual MSU pairs are of different length.  
     
     
         47 . The system of  claim 44 , wherein a pilot word dual MSU pair has a different length than a payload dual MSU pair.  
     
     
         48 . The system of  claim 40 , wherein the burst organization block (f) is further configured to: 
 i) organize data intended for transmission into a frame structure that includes a burst preamble followed by a payload,    ii) incorporate a preamble pilot word having a length PrePW within the burst preamble,    iii) incorporate payload dual MSU pairs that are unknown to the receiver into the payload, and    iv) incorporate a payload pilot word having a length PayPW within the payload.    
     
     
         49 . The system of  claim 48 , wherein PrePW≠PayPW.  
     
     
         50 . The system of  claim 48 , wherein the burst organization block (f) is further configured to vary a length of pilot words disposed in similar relative positions within different frame structures, and/or to vary a number of pilot words disposed in such different frame structures, depending upon an indication of transmission quality.  
     
     
         51 . A receiver system for receiving paired multiplexed signals transmitted from plural antennas, the system comprising: 
 a) a receive and alignment block configured to receive and align prefixed multiplexed-signal-units (“MSUs”) received sequentially in a frame structure having a preamble portion and a payload portion;    b) a cyclic prefix removal block configured to remove cyclic prefixes from received MSUs;    c) a pilot word identification block configured to identify, in accordance with relative position within the frame structure, J concatenated copies of a first received pilot MSU, RP 0 , followed by P concatenated copies of a second received pilot MSU, RP 1 , that were transmitted based upon a first expected pilot signal-unit EP 0  and a second expected pilot signal-unit EP 1 ; and    d) a channel estimation block configured to combine a representation of RP 0  and a representation of RP 1  with complex conjugated forms of EP 0  and EP 1  to create a first channel estimate H 1 , and to combine the representations of RP 0  and RP 1  with forms of EP 0  and EP 1  that are not complex conjugated to create a second channel estimate HE 2 .    
     
     
         52 . The receiver system of  claim 51 , wherein the pilot word identification block is further configured to average the J concatenated copies of RP 0  to form the representation of RP 0 , and to average the P concatenated copies of RP 1  to form the representation of RP 1 , and wherein J≠1 and/or P≠1.  
     
     
         53 . The receiver system of  claim 51 , wherein J=P≠1.  
     
     
         54 . The receiver system of  claim 51 , wherein J≠P.  
     
     
         55 . The receiver system of  claim 51 , wherein the J concatenated copies of RP 0  have a length different from a length of a payload MSU.  
     
     
         56 . The receiver system of  claim 51 , wherein a length of RP 0  is less than a length of a payload MSU, and further comprising an interpolation block for deriving from the representation of RP 0  a signal-unit having a length equal to the length of a payload MSU.  
     
     
         57 . The receiver system of  claim 51 , the pilot word identification block is further configured to identify the J concatenated copies of RP 0  and the P concatenated copies of RP 1  within the preamble portion of the frame structure, and to identify K concatenated copies of a third received pilot MSU RP 2  and L concatenated copies of a fourth received pilot MSU RP 3  within the payload portion of the frame structure.  
     
     
         58 . The receiver system of  claim 57 , wherein K≠J.  
     
     
         59 . The receiver system of  claim 57 , wherein each payload MSU is an N-point OFDM symbol.  
     
     
         60 . The receiver of  claim 57 , wherein each payload MSU is an N-sample block of single-carrier signals.